Question

Hi can someone help me with this table and graph stuff for algebra?

Answer 1

I guess it could be either linear or cubic. It kind of looks like there's an inflection point between 1974 and 1975.

Do you have to find the equation by hand?

Answer 2

it doesn't really say, but it would probably be for the best.

Answer 3

ok well if you have to do it by hand, it's probably linear.
least square regression?

Answer 4

It doesn't say specifically but that should work.

Answer 5

you have to change your table to do this.
The y-column is fine the way it is.
The x-column needs to start at 0. So let 1885 be year 0 and let x be years after 1885. So like 1917 will be 32, 1919 will be 34, etc

Answer 6

okay wait I think I misinterpreted what you typed. I have to change the table to find an equation?

Answer 7

Yeah, we're looking for an equation in y = mx + b form. If you leave the table like that it will skew the y-intercept ( I believe)

Answer 8

right okay I think I follow you a little.

Answer 9

this is making the gears in my head spin lol I know the equation has to be y=mx + b

Answer 10

This is one I helped someone with last night. Scroll to about the middle of the page. Do the formulas for a and b look familiar?
http://openstudy.com/users/peachpi#/updates/55d7dbd9e4b02663346b9fa8

Answer 11

oh yeah! I've seen those before. I mean I always get the numbers mixed up. I wouldn't know where to put what.

Answer 12

that's fine. Just start with adjusting the years and we'll go from there

Answer 13

I feel like that table on that page or whatever has specific numbers for the x's and y's. I wouldn't know which ones to apply for my situation.

Answer 14

Your y's are going to be the stamp's costs (0.02, 0.03, 0.02, 0.03, etc.)
Your x's are going to be years since 1885 (0, 32, 34, 47, etc). Subtract 1885 from each year to get these

Answer 15

oh that's how you got those, ok.

Answer 16

If you have excel, google docs, or some other spreadsheet program it will do the calculations for you and you just have to arrange the table

Answer 17

I had excel but the trial ended. I don't really have any way to do this. I don't know I gotta think about this.

Answer 18

for that girl you did a table that was x|y|x^2|xy is that what I have to do?

Answer 19

yeah

Answer 20

oh man okay x would start with 0? I think you said. I'm sorry I'm so hopeless I'm getting myself confused all over again.

Answer 21

or would the x and y columns look exactly like my table? and then I would multiply x by itself and then I multiply x and y?

Answer 22

hold up. I don't think those are going to be the right equations anyway.
I think this might be exponential. It just doesn't look so on your graph because the years aren't evenly spaced. This is what I get with an evenly spaces x-axis

Answer 23

so I did my graph wrong? Or that's a new graph over my original graph?

Answer 24

no, your graph is wrong. You used 1 square for each difference in years, but the differences aren't all the same

Answer 25

so do I need to redo the years on my graph? I actually wasnt sure how to space them. I only had like 25 spaces. Yeah the years aren't spaced correctly.

Answer 26

what spacing would you recommend I use?

Answer 27

I can use the spacing you used for the y axis, but I'm not sure for the x axis.

Answer 28

Ok so we're going from 1885 to 2012, that's 127 years. Divide by 25 to get 5.02, so make every space 6 years to have a little extra room on the right

Answer 29

Don't put the actual years on the graph.
so start at 0, then 6, 12, 18 etc.
Then use a label that says "Years since 1885"

Answer 30

I'm sorry for being so confused. I'm really trying to understand this

Answer 31

so i didn't label the years but started with 0 and ended with 138 (that's as far as my graph will let me go)

Answer 32

0 represents 1885. 6 represents 1891. 12 represents 1897. Even though 1891 won't be a point on the graph, we have to show it on the x-axis to show how long it's taking the price to rise at the beginning.

1917 is 32 years after 1885. So that point will be about 5 or 6 grid lines right of the first point

Answer 33

okay I'm gonna need a much bigger graph

Answer 34

No your graph is fine. 2012 is 127 years after 1885.
Your graph is showing 138 years after, so we have a little extra.
That's exactly what we want

Answer 35

okay

Answer 36

Have you done the thing where you subtract 1885 from all the years yet?

Answer 37

is the y axis okay? I went by 2's on there?

Answer 38

yes the y-axis is good

Answer 39

I wasn't sure what you meant by that.

Answer 40

like this
1885 - 1885 = 0
1917-1885 = 32
1919 - 1885 = 34

Answer 41

oh okay well I'll do all those and get back to you okay?

Answer 42

ok.

Answer 43

almost done...

Answer 44

ok

Answer 45

ok. At the bottom of the page are the equations for curve fitting an exponential function (lowercase a and b).
http://mathworld.wolfram.com/LeastSquaresFittingExponential.html

Answer 46

then I need to square the x's and then multiply x and y

Answer 47

oh man yikes okay

Answer 48

this one isn't linear so the equations are different.
Have you seen those before?
I had a hard time even finding them, so I'm wondering if you're supposed to do this using technology as opposed to hand

Answer 49

No I haven't really seen them before (hence my yikes lol) This is on a worksheet so I just assumed it was by hand

Answer 50

I feel like my heads gonna explode.

Answer 51

If you have or want to create a google account, google docs will calculate the curve once you enter the data in their spreadsheet

Answer 52

I just have a really hard time thinking they want an algebra student to do this by hand :/

Answer 53

I've never used spreadsheets before. How do I see the curve in the spreadsheet?

Answer 54

you have to enter the table and then create the chart. I can walk you through it. Search for google docs then sign in to create a spreadsheet

Answer 55

okay I'm on the spreadsheet (that link you gave me that you did last night since her graph thing was linear and my is expo than how I find an equation is different?

Answer 56

Linear is y = mx + b

Exponential is \(y=ab^x\)

Answer 57

okay gotcha well i'm on the spread sheet now

Answer 58

can you explain to me why it is expo? I don't think we went over that

Answer 59

ok. so now make columns for x and y. Put the x column to the left and enter the numbers you got by subtracting (0, 32, etc) and another for the prices

Answer 60

make the correct graph first. It will be easier to understand that way. You really wouldn't know whether it was linear or exponential once you see the graph.

Answer 61

*until you see the graph

Answer 62

so in the A column put
0
32
34
47
all the way ↓ to
127

In the B column
0.02
0.03
0.02
0.03
↓
0.45

Answer 63

okay let me do all of that

Answer 64

I labeled the two sides of the table (years were x) (y were costs)

Answer 65

okay now what do I do?

Answer 66

ok. now highlight the cells with numbers in them and go to the INSERT menu at the top and select CHART

Answer 67

stupid question - how do I highlight them w/o highlight the little grey column on the left?

Answer 68

That's going to highlight automatically so you know which cells are selected. It's fine.

Once you pick Chart A box should pop up with named Chart Editor with Recommendations, Chart Types, and Customization tabs

Answer 69

I don't think it matters

Answer 70

ok

Answer 71

okay I did insert and selected chart

Answer 72

i'm in the chart editor

Answer 73

One of the recommended charts should a grid showing dot. Select that one and hit INSERT at the bottom

Answer 74

okay

Answer 75

done

Answer 76

do you want me to screencap and upload it to make sure it looks good?

Answer 77

yes please

Answer 78

not sure if that looks right

Answer 79

This is mine

Answer 80

hm seems like I missed something

Answer 81

For the most part it looks right. Maybe one of us made a typo when entering the points

Answer 82

yeah could be. I really don't think they will notice too much. it's fine

Answer 83

I'll leave it to you to check, but we can go on so you know how to get the equation

Answer 84

okay

Answer 85

Do you notice how it almost flat toward the left and then increases steeply toward the right? That's how I know it's exponential

Answer 86

right